A description of different types of accommodative and non-accommodative esotropias, including fully accommodative and partially accommodative esotropias and convergence excess esotropias.
Accommodative esotropias are a group of convergent squints that usually develop between the ages of 18-36 months of age. Frequently there is a family history of a squint, childhood refractive error (usually long sightedness) and / or amblyopia.
Children who develop an accommodative squint are invariably long sighted and as a result of their long sightedness they have to exert extra focusing to bring a near object into sharp focus.
When we look at an object close to us our eyes turn inwards to look at the object (this is called convergence) and the eyes adjust their focus to form a clear picture of the object (a process known as accommodation). The amount of convergence and accommodation are directly linked, so that we can see a clear single image of what we are looking at.
If a child is long sighted they have to accommodate more to bring a close object into sharp focus, but as a result they will automatically converge more than is necessary and they may develop an accommodative esotropia.
Initially the child will have an alternating squint, which means they will use their right eye one minute with their left eye turned inwards and then swap to use their left eye, with the right eye turning inwards. However, many children very quickly tend to favour one eye over the other and will permanently switch off (suppress) the image from the in turned eye, causing this eye to become amblyopic.
If the angle of the esotropia is fully corrected with glasses the squint is said to be a “fully” accommodative esotropia. These children normally have excellent stereopsis and do not develop amblyopia.
If the angle of the squint is not fully corrected with glasses it is called a “partially” accommodative esotropia.
Some children have a large angle convergent squint when they are looking at a near object, but their eyes are straight or almost straight when they are looking at a distant target. This is known as a convergence excess esotropia. Children with this form of esotropia potentially have good stereopsis if their squint is corrected, with bifocal glasses or surgery.
If there is no change in the angle of the squint with long sighted glasses the squint is said to be a non-accommodative esotropia.